On radar cross-section of the Sun during earthward-directed CME
Abstract
In order to design radar experiments for the study of the Sun, it is necessary to make some preliminary estimates. We report results of crude calculations of the solar radar cross section during the appearance of a geoeffective CME. For the calculations, we consider the CME to be a spherical expanding plasma shell with a constant mass moving towards the Earth. Two approximations --- ``mirror reflection'' and ``volume scattering'' --- were used. The dependence of the radar cross-section on amount of mass ejected, expansion speed, velocity of the motion away from the Sun, as well as sounding frequency were obtained. In the ``mirror reflection'' model during geoeffective CME the cross-section should first drops at the moment when the CME leading edge achieves the critical level in the solar corona, at which plasma frequency is equal to the sounding frequency. Then the cross-section slowly increases until the decreasing plasma frequency at the leading edge of the expanding CME becomes less then the sounding frequency. After this, the cross-section attains the value for the quiet Sun. For the ``volume scattering'' model a decrease of the gross section after the leading edge achievement of the critical level is much slower. The effect described could be observed by a solar radar operating in approximate frequency range 10--50 MHz. Criteria of the CME geoefficiency determination with the use of solar radaring are discussed on the base of the results obtained.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....8582B